Shell broach



J. A. PSENKA SHELL BROACH April 20, 1965 '7 Sheets-Sheet l Filed April 1o, 1961 ON ON INVENTOR.

JOSEPH A. PSENKA TORNEYS J. A. PSENKA April 2o, 1965 SHELL BROACH 7 Sheets-Sheet 2 Filed April lO, 1961 FAM E :mi

OUII -l -i I INVENTOR. JOSEPH A. PSENKA J. A. PSENKA I April zo, 1965 SHELL BROACH '7 Sheets-Sheet 5 Filed April l0. 1961 wm vm INVENTOR. JOSEPH A.PSEN KA MMM/.M @gif/4,1%

TORNEYS April 20, 1965 J. A. Psx-:NKA 3,178,800

SHELL BROACH Filed April lO, 1961 '7 Sheets-Sheet 4 if! u.

INVENTOR.

JOSEPH A. PSENKA BY MM@ MM Q/e f ATTOFI NEYS April 20, 1965 J. A. PSENKA 3,178,800

SHELL BROACH Filed April l0, 1961 7 Sheets-Sheet 5 i) (D i mili O m. llmlnm Ll.

LN In mi N 9 Ll.

CD g

INVENTOR. JOSEPH A PSENKA q1' jala 'f7 ATTORNEYS April 20, 1965 J. A. PsENKA 3,178,800

SHELL BRoAcH Filed April l0. 1961 '7 Sheets-Sheet 6 J. A. PSENKA April 20, 1965 SHELL BROACH 7 Sheets-Sheet 7 Filed April lO. 1961 FIG.3I.

INVENTOR. .JOSEPH APSENKA United States Patent O 3,173,899 SHELL BRGACH Ioseph A. Psenka, Bloonn'icltl Hills, Mich., assigner t0 National Breach & Machine Qompany, Detroit, Mich., a corporation of Michigan Filed Apr. Il), i961, Ser. No. Itil? 5 Claims. (Cl. .Z9- 951) The present invention relates to a broach and more particularly, to a broach comprising a plurality of sections, a leading one of which is a roughing section adapted to rough out the teeth of a gear or splined element, and a following section oi which is a finishing section adapted to finish the teeth of the workpiece with extreme accuracy.

Broaches of the type described have been utilized in the industry. However, certain problems have been encountered. One ot the main problems is that the side of the part which is produced by the obtuse side of the broach has more stock removed from it than from the side of the part which is produced by the acute side of the broach. This usually results in the acute side not cleaning up fully so that the errors of form introduced into the part by the roughing section of the broach are not entirely corrected or eliminated by the side shaving shell forming the finishing section of the breach.

The present invention relates primarily to different ways of correcting errors of form in the broach part which are introduced into the part by the roughing section of the broach. This is accomplished by providing an improved side shaving shell which is adapted to be mounted at the rear of the roughing section of the broach so as to completely remove the aforesaid errors.

It is an object of the present invention to provide a full form finishing broach of the character described in which the inishing section is connected to the leading roughing section in such a manner that the finishing section will locate itself accurately in the workpiece and will therefore produce teeth on the workpiece which, for practical purposes, have the same accuracy as the teeth on the finishing section ol' the broach.

Another object of the present invention is to provide a full form iinishing broach which includes a side shaving shell that has on the front hall of the side shaving shell cutting teeth in which the obtuse sides thereon are straight so as to actually follow the helix without any backoi'i angle and the acute sides thereon are backed o to provide the cutting and on the rear halt `of the shell the acute sides of the cutting teeth are straight so as to become guiding teeth and the obtuse sides are backed ofi 'to perform the cutting.

A further object of the present invention is to provide a full form linishing broach which includes a side shaving shell having the teeth thereon so arranged as to equalize the amount of stock removal from both the acute and the obtuse sides.

A still further object of the present invention is to provide a loroach which has a side shaving shell thereon wherein the teeth thereof are arranged so that the backoii .angle on the acute side is greater than the backoff angle on the obtuse side so as to increase the resistance of the tool to move into the obtuse `side of the part.

Still another object of the present invention is to provide either an internal or external broach having a inishing section wherein the leads on the obtuse and acute sides of the teeth are decreased from the true lead so that the obtuse side produces a counter force to the natural rotative force that the acute side produces to pull the part into the obtuse side, thereby balancing stock removal from the brosch part.

Still another object of the present invention is to provide a full form finishing broach which has a roughing ice section and a finishing section which is adapted to tit tightly on the roughing section so as to prevent relative movement between the roughing and finishing sections.

Other objects and features of the invention will become apparent as the description proceeds, especially when taken in conjunction with the accompanying drawings illustrating preferred embodiments of the invention, wherein:

FIGURE 1 is a side elevation of the broach assembly.

FIGURE 2 is a side elevation of the leading roughing section of the broach.

FEGURE 3 is an end View of the leading section of the broach seen from the right in FIGURE 2.

FIGURE 4 is an enlarged view of adjacent teeth illustrated in FIGURE l taken on the line 4 4 thereof.

FIGURE 5 is an enlarged view of adjacent teeth illustra ed in FIGURE l taken on the line 5 5 thereof.

FEGURE 6 is an enlarged side elevation of a side shaving shell.

FIGURE 7 is a right hand end vier of the shell shown in FIGURE 6.

FIGURES 8-10 are various modifications of a iinishing tooth having the acute side backed ofi.

FIGURES 1I-13 are various modifications of a finishing tooth having the obtuse side backed oli.

FIGURE 12A is a front View of the tooth looking in the direction of arrow 2-A-*l2-A of FIGURE 12.

FIGURE i4 is a diagrammatic plan view of a portion of a workpiece illustrating the generating lines caused by the teeth oi the broach.

FIGURE 14A is a diagrammatic View of the profile of the broach part illustrating the traces of the teeth of the broach.

FIGURE l5 is a side view of a pair of adjacent teeth looking in the direction of line lS-IS of FIGURE 6.

FGURE 16 is another embodiment of the side shaving shell showing the elevation thereof.

FIGURE 17 is an end view of the shell down in FIG- URE 16.

FIGURE i8 is a view of the teeth looking in the direction of line it-i8 of FIGURE 16.

FIGURE 18A is a diagrammatic view of a side shaving iinishing tooth.

FIGURE 19 is a side elevation of still another embodiment of the side shaving shell.

FIGURE 20 is an end view of the side shaving shell shown in FIGURE 19.

FIGURE 21 is a view of adjacent teeth of the side shaving shell looking in the direction of line 21-21 of FIG- URE 19.

FIGURE 22 is a diagrammatic representation illustrating the deviation of the leads on the acute and obtuse sides from the true lead center line of the side shaving shell.

FIGURE 23 is a side elevation of still another embodiment of the present invention.

FIGURE 24 is an end view of the side shaving shell shown in FIGURE 23.

FIGURE 25 is a View of adjacent teeth looking in the direction of line 25*25 of FIGURE 23.

FIGURE 26 is a fragmentary sectional view showing the relationship between the side shaving Shell and the roughing section.

FIGURE 27 is a sectional elevational view of a iinishing shell which is adapted to finish external parts.

FIGURE 28 is a right hand end View of the shell shown in FIGURE 27.

FIGURE 29 is a view of longitudinally aligned teeth looking in the direction of arrow 29-29 of FIGURE 27.

FIGURE 30 is a fragmentary elevational view showing the last row of cutting teeth on the roughing section in line with the teeth on the pilot of the iinishing shell.

FIGURE 3l is an elevational View of a finishing shell having a staggered or differential pitch which illustrates another modification of the present invention.

FIGURE 32 is a diagrammatic illustration illustrating the manner in which the entering tooth of the finishing section contacts the form produced by the roughing section.

In the breaching of internally toothed members, such as internal gears, spline members or the like, it is possible to produce breaching elements having substantially any required degree of accuracy. However, in use, such a breaching element can reproduce itself with substantially perfect accuracy only when it is not subjected to negative factors occasioned by an earlier stage of the breaching operation. The present invention relates to a breach which has a roughingsection and a finishing section, with the nishing section taking the ferm of a replaceable side shaving shell which is affixed to and located on the rear end of the breach body following the roughing section, such as disclosed in my Patent 2,987,801 which issued on J une 13, 1961. Certain aspects of the invention may be embodied in a finishing breach construction whether formed as a part of a breach including the finishing construction or formed as a separate breach.v Y

Referring now to the drawings, the leading section of the breach assembly 10 is shown in FIGURES l and 2 and is designated by the-numeral 11 and comprises a head 12 adapted to be connected to a suitable device for pulling the breach through a hole in a workpiece. rConveniently, the roughing section of the breach is indicated generally at 14 and includes a series of continuous interrupted annular blades or ribs 16 adapted to form separate cutting teeth 20. The rear part of the roughing sec- 1o is to form a spur member and the series are helically aligned if the breach 16 is used to produce helical teeth on the workpiece. At the leading end of the finishing section 4d, a notch or keyway is provided which extends diametrically across the leading end thereof and is dirnensioned to receive the key 38 at the following end of the roughing section of the breach. The finishing seetion 40 is generally provided with a central opening, the intermediate portion of which is enlarged to provide clearance and the ends of which are of slightly reduced size to provide guide surfaces which are guidingly received on the cylindrical surface of the support portion 220i tion includes alternate round and spline teeth. The round t teeth or blades 18 are adapted to machine the hole in the workpieceto true cylindrical formation.V The spline cutting teeth 20 are progressively stepped from front to rear and are backed off on the top at an angle phi and the sides thereof are relieved to Within 1A.; inch to 3&4 inch of the top of the profile. The roundrteeth 18 are also backed off at an angle alpha.

It will be appreciated that the cutting teeth 20 are arranged in axial alignment if the breach 10 is for the purpose of producing spur teeth, or in helical alignment if the breach is for the purpose of producing helical teeth. The term longitudinal alignment or the like is intended to cover arrangements for producing both spur and helical gears.

At the following end of the roughing section 14 of the breach assembly 10 is a cylindrical support 22 having a reduced portion 24 which forms a shoulder 26. Rearwardly of the reduced portion 24 a support portion 22 is threaded as indicated at 28. Rearwardly of the threaded portion 28 is provided a cylindrical support-portion 30.

Directly to the rear of the final blade of the roughing section 14 there is a cylindrical surface 32, the opposite sides of which are machined away as indicated to form rearwardly facing flat abutment surfaces 34 and radially outwardly facing fiat surfaces 36. This arrangement provides a fiat transversely extending key 38. As shown in FIGURE l, the following finishing breach section or side shaving shell is assembled on the support portion 22 of the leading section 11. Rearwardly of the finishing section or shell 40 is located a spacer 41 followed by a round shell 42 comprising a plurality of continuous 'Y part from drifting into it.

the leading section 11 ofthe breach 1G.

It willbe observed in FIGURE 1 that the nut 423 has the front portion or forwarder-id thereof-engageable with the rear end of the round shell 42 so as to urge the spacer 41 into engagement with the shoulder 26. With such a key and keyway construction between the roughing and finishing sections a small clearance in the amount of .G02 inch is sufficient to permit limited circumferential relative movement between' the roughing and finishing breach sections. In addition, the key and keyway constructions of the sections are properly related with respect to the cutting teeth thereon so that they cutting teeth 52 on the finishing section are in substantial true alignment with the teeth 2t) of the roughing section. Nevertheless, as the finishing section 4) moves into action, it is permitted to float so that it alignsitself with substantial perfect accuracy with Vrespect to the teeth as partially roughed out by the roughing sectionof the breach. The teeth 52 of the finishing section 4t) are of less height than those of theroughing section and hence, cut only on the sides. The top portions of the teeth52 are thus able to pass in clearance through the grooves or slots provided at the bottom ofthe tooth spaces cut by the roughing section. The widths of the side shaving teeth' increase from front to rear. The broach'assembly just described is disclosed in the aforesaid Patent 2,987,801.

Certain problems have been encountered with the use of side shaving shells 40 of the type just described in that the side of the part which is produced by the obtuse side of the breachhas moreV stock removed from it than from the side of the part which is produced by the acute side of the breach. This results sometimes in the acute side not cleaning up entirely sethat the errors of form introduced into the breach part by the roughing section are not eliminated by the side shaving shell in a practical length of shell.

In order te compensate for this particular condition, the amount of stock removal on the circular tooth thickness has been increased from .002 inch to .G05 inch. In addition, an entirely new approach in design is utilized such that en half the cutting teeth of the shell the obtuse side will be straight without any backotf angle so as to actually follow the helix and the acute side thereon is backed ed to provide the cutting. The straight obtuse side provides a control side and as the breach moves along through the part, the obtuse side keeps or prevents the Due to the fact that the obtuse side has ne backoff angle, the cutting is accomplished entirely on the acute side. On the remaining or rear half of the breach, the acute side is straight with no backoff angle and provides a control side which keeps the part from drifting into it while the obtuse side is backed olf and provides the requisite cutting action. In this manner, the amount of stock removal from both the acute and obtuse sid-es is equalized.

FIGURE 6 shows a side shaving shell 60 which is adapted to fit on the roughing section in the manner similar to that described for FIGURE l. Line A-A of FIG- URE 6 divides the shell 60 into two `halves or parts of substantially equal widths which are designated by the numerals 62 and 64. The obtuse sides of the longitudinally aligned side cutting teeth 65 are represented diagrammatically by the line 66. The acute sides of the longitudinally aligned side cutting teeth 65 are diagrammatically represented by the line 53. In the shell part d?. of the side shaving shell 69, the obtuse sides are straight with no backoif angle, thereby providing guiding action, while the corresponding acute sides are backed off and provide the requisite cutting action. The reverse is true for the breach part 64 in that the obtuse sides are backed ofi and provide the requisite cutting, while the acute sides are straight and provide the necessary guiding action.

FIGURES 8-10 represent the construction or" a tooth 6l in the fhst half or part 5.2 of the shell di?. FIGURE 8 shows a tooth 51a having a cutting edge 79, with the acute side thereof backed ofi at an angle Phi. The obtuse side of the tooth ola is straight so as to provide guiding action to prevent the broach part from drifting into the acute side.

FIGURE 9 shows another modification of the tooth designated by the numeral b. The cutting edge 72 has a chamfer '74 which insures that there will be no cutting action on the obtuse side. The acute side of the tooth @Ib is backed olf at an angle Phi. While the cutting edge .72 has a chamfer 74, it should of course be understood that chantier 7d may be rounded or take another form or shape so as to prevent cutting action on the obtuse side of the tooth olli.

FIGURE 10 is still another modiiication of the tooth 61!) as represented by the numeral 61C. The tooth el has a cutting edge '76 which has a long lead 7S on the obtuse side, with only approximately 1/16 or 1/s of an inch of the obtuse side, as represented by the numeral 89, providing the requisite guiding action. The advantage of this., construction over a straight chamfer or a round corner, as .escribed for FIGURE 9, is successive face sharpenings on a broach utilizing a long lead does not require additional worlf` chamfering the side of the tooth proiile. With the construction shown in FIGURE 9, the chamfer 74 would have to be put back on the tool or broach after enough face sharpenings have been made on the bro-ach to remove it. The length of the obtuse portion 89, which provides the small amount of guide surface, will depend upon the particular application. In any event, enough guide surface Si) has to be present to prevent metal pickup on the obtuse side. However, in certain applications, if the long lead 78 can be incorporated without metal pickup, it would be more desirable from a maintenance standpoint than to have very abrupt cham fers at the face of the breach.

FIGURES 11-13 represent modifications of the tooth as contained in the rear half or part 64 of the shell 5t). Tooth 61d has a baclroif angle Phi on the obtuse side, with the acute side being straight and providing the requisite grinding action.

In FIGURE l2, a tooth 61e is backed off on the acute side and the cutting edge thereof, as represented by the numeral 8d, has a chamter 81 so as to prevent metal pickup. The remaining portion of the acute side is straight so as to provide the requisite guiding action. This figure is similar to FlGURE 9.

FIGURE 13, which is similar to FIGURE i0, has the obtuse side backed off at an angle lhi, with the acute side having a long lead 82.

Referring now to FIGURES 14 and 14A, there is diagrammatically illustrated the manner in which the eeth of the broach moving through the workpiece 3d in the direction of the arrow produce a plurality of generating lines as represented by numeral 86. The generating lines occur on the acute side and result 'in a rounding off of the profile as indicated at 88 in FIG- URE 14A. As a result of the drift, the side of the tooth space which was cut by the acute cornered sides of fthe broach teeth is deformed as indicated by numeral 88. Thus, both lead and proiile of the broach surface are ink error. On the other hand, the side produced by the acute side of the breach shows no error and is correct throughout as to lead and profile.

FlGURE 16 shows a modication of the finishing shell and is designated by the numeral 9i). Shell 9) has a series of longitudinally aligned side cutting teeth 94 which progressively increase in width. In order to prevent the obtuse side of the roach shell 9i) from removing more material from the part on circular tooth thicknesses than the acute side, it has been found that changing the backoii angle on the acute side will be of some benet in correcting the errors of form. FIGURE 18A shows a tooth 94a having a cutting edge 96, with the acute side backed oli at an angle Phi and the obtuse side backed off at an angle Alpha, with the angle Phi being greater than the angle Alpha. With such a construction, the greater the backoff angle on the acute side, the freer will be the cutting action tl ereon and the less tendency there will be to pull the part into the obtuse side and conversely, the lower the baoltot angle on the obtuse side, the greater will be the tendency for resistance of the breach to move into the olbtuse side of the part.

Originally, finishing shells of the type described had a three-quarter degree baclio angle on both the acute and obtuse sides of the teeth for both spur and helical. However, due to size reduction of the tool with successive face grinding/s that produced undersized parts in a relatively short time, the backotf angles were decreased to one-half degree on both sides of the teeth on both spur and. helical applications. With the present invention, it has been found that the aforesaid problem is substantially eliminated by decreasing the obtuse baclioff angle to one-quarter degree and increasing the acute backotf angle to three-quarter degree. The net result is a broach that has as much tool life as if both sides were 'backed oil to one-half of a degree.

FIGURE 19 shows another modification of the side shaving `shell which is represented by the numeral wl. The shell itil? has a series of longitudinally aligned helical teeth tZ. In the past, the teeth lill have followed a true lead center line as is diagrammatically represented by the line ldd. With this type of prior art construction, the obtuse sides of the teeth were on a true lead as is diagrammatically represented by the line 106. Also, the acute sides of the teeth were also on a true lead as represented by the line 163. However, with such a construction, it was found that the obtuse side of the teeth 192. removed more stock from the part on circular tooth thickness than the acute side. In order to correct the errors, it was found that it was desirable to change the leads on the teeth from true leads as just described so as to actually produce a counter force to the natural rotative force that the acute side is producing. This is accomplished by decreasing the lead on the obtuse and acute sides of the teeth. In other words, the helix angle on the acute and obtuse sides is increased. However, the total amount of stock removal is the same as if true leads are actually present. By incorporating the changes in the leads, the obtuse side presents a counter force that balances out the natural tendency of the acute side to pull the part into the obtuse side. Described in another manner, the center line of the tooth is adapted to move at a different lead than the breach itself is moving or turning. the acute side which represents on olf lead condition is represented by the numeral Iltl, while the oli" lead condition in the obtuse side is represented by the numeral i12. With such a construction, the amount of oli` lead of the obtuse side is greater than the amount of oil lead on the acute side and is shown in FIGURE 19 by the relationship of X to Y in which X is greater than Y.

With the present invention, the lead on the obtuse side and acute side would be shorter than that caused by the normal cut per tooth. The center line of the teeth would be on a shorter lead. FlGURE 22 diagrammatically illustrates the longitudinally aligned first and last teeth on the shell represented by the numerals 114 and Tilo respectively. When the teeth are on the true lead center line ldd, X1 equals Y1. However, when the teeth are not symmetrical about a true lead center line, X is arranco greater than Y as'previously described. In each case shown, X plus Y equals Z and X1 plus Y1 equals Z where Z is the total stock removal. This embodiment provides a broach having finishing teeth in which the center line of the iinishing teeth traverses a leajd path divergent from the path which the broach properjis traversing.Y

As previously described, the finishing shell is adapted to float with reference to the roughing section. However, in the embodiment shown in FIGURE 26, leading section 11 has a fiat transversely extending key or tang 38 as in the other embodiments. 'Howeven the finishing section or shell 12.0 is provided with a notch or keyway 124 which isY of a size so as toV tightly grip the key or tang 38 on the roughing section, thereby preventing circumferential and axial movement betweenv the iinishing and roughing sections as in the other embodiments.

In addition, the. first tooth of the shell 12) is a cutting tooth 126 backed off on the sides. Heretofore, the first tooth has served as a pilot. Thetooth 126 is reduced on circular cross section and issmaller than any of the other longitudinally aligned teeth 128 of the roughing section.

Such a construction reduces the possibility of any'loss of control and any unnecessary movement of theshell 120.

FIGURE 27 shows a shellhroach 130 for producingvv external parts., The shell broach 139 is adapted to follow either a generating type shell, a Fellows gear'shaped Vgear ora hobbed gear. The longitudinally aligned finish cutting teeth 132 increase in'tooth width from the front of the shell to the rear, the amount of stock removal Vbeing dependent on this increase in tooth width The sides of the teeth arebacked ofi sharp.

The backoti angles Phi and Alpha are the b-ackoti angles of the obtuse and acute (sides of the teeth respectively. The backolf angles may be equal orof greater magnitude one to the other. The center line of thek teeth v132 may either follow a true lead or a higher or lower than true lead.

The broach shell 130 is divided in hal-f about line B--B so that on rthe -forward half or part 134 of the shell 130,

The iirst tooth 138 of the broach may be either a pilot Y tooth, that is, a non-cutting tooth with an entering lead, or it may be an exceptionally heavy bumper tooth backed off on the sides to initiate some cutting. i

Another problem which has been encountered with the side shaving shell broaches has been that the front pilot off the shell constituted a dwell area in which a part, if it were sufiiciently short in length of cut, might possibly be free to fall upon the front pilot. This of course is undesirable for pull-up machines in that if the part would drop away fnom the base plate fixture, chips fall or might be washed in on top of the part. When the shell begins its cutting action and brings the part up tothe face plate fixture, an off lead condition results in the part.

In order to overcome thisobjectiorn, I have devised a o c: on .a leadingroughing broach section 11, as shown in FIG- URES 1 and 2, which is provided with alternate round and spline cutting teeth 18 and 16 respectively. The end view of the shell 16) is similar t-o FIGURE 24.

A problem has been encountered in side shaving shell breaches wherein surge marks result in the protile of the broach part along its length. With the type of broach just described, the pitchof the broach is uniform so that the surge marks in the broach part are spaced apart at an equal distance.

The surge marks are caused Iby the fact that a varying number of Iteeth are in the workpiece at any moment. The teeth will vary in the vfollowing manner: in one instance, for example, a'm-aximum of four teeth and a minimum of three teeth are in the workpiece; as another example, a situation may result where a maximum of two teeth and a mini-mum of only onetooth are provided in the workpiece. Under these conditions there are load changes on the broach land on the machine from to 50%. Since the pitch of the teeth is heldpunifo'rmly, the broach force load changes occur at very specific positionsl when the teeth are in .the workpiece. monic marks.V y

In order to `alleviate this condition, a staggered pitch or differential pitch is provided inthe side shaving shell 160. In other words, the pitch from tooth to toothis not uni- V form. The use of a differential pitch on the side shaving Vshell 16) results in a condition in which the longitudinally aligned teeth 162k of the side'shaving shell 160 do not always sur'ge at the same point in the breached part. The teeth-1612 areV also arranged in circumferentially aligned groups of progressively increasing width and height. The

corresponding edges at .bothsidesfof the teeth are circumferentially stepped so as to `cut on the sides thereof.

- The side shaving shell 160 maybe adapted for a multiple pitch construction. As examples, both a double staggered pitch and -a triple staggered pitch broach are illustrated.- The double Vstaggered pitch broach, for example, may be of the type Where the pitch A equals 1/2" and the pitch B equals W16. InA a triple staggeredV pitch broach, as an example, C equals 1%2", D equals 1/2 and E equals 17/32. The pitch distancesare alternately repeated longitudinally of the broach as illustrated. It should be understood that this invention is also :applicable to quadruple pitch bronches.y

This approach hasV proved very elective in controlling surge marks in round hole broach applications since the Y teeth do not always surge at the same point in-the workstructure, a part of which is shown in FIGURE 30,

FIGURE 31 illustrates another modication of the present invention. The improvement relates specifically to the side shaving shell 160 which is adapted to be mounted piece. In addition, this invention is also :applicable to side shavingshells or to solid side shaving breaches which have alternate round and. spline teeth wherein the pitch otkboth the round teeth and the side shaving spline teeth is varied. y

FIGURE 32 is a diagrammatic illustration of how the first entering finishing tooth of a 'broach cuts the 4form of the tooth space produced by the roughingV teeth.

This may be accomplished by utilizing a broach which has a roughing section Vand a finishing section which can either be an integral part of the broach, in other words, a solid one-piece broach, or i-t may have a replaceable finishing shell which is -aflixed to land located on the rear end ofthe broach body following the roughing section. The finishing section of the broach may |have either ,alternate interrupted and uninterrupted cutting blades lor only interrupted blades, with the interrupted yblades -forrning longiltudinally aligned series rof teeth. The longitudinally aligned teeth increase in width from the leading end to the following end of the linishing section. The first finishing tooth cuts only -a portion of the profile or form near the minor diameter thereof. As fthe broach cuts circumferentially, the next succeeding teeth increase in width so as to gradually cut more of the prole until lfinally the remainingnishing teeth encompass the entire proiile up to :the major diameter.

As an example, a side shaving shell broach or a solid 'brOah is utilized which is constructed and arranged so This results in surge or harthat the nishing teeth cut the `form 164 of the tooth space in the workpiece 162. The form 164 is produced by the roughing teeth of the broach. The iirst entering tooth of the finishing broach is represented by the dotted line 166 and contacts the tooth form 164 at points A so as to remove the triangularly shaped materia-l 168 from .the form 164. With such a construction, the iinishing tooth 166 starts cutting near the minor diameter of the broach. The succeeding finishing teeth out in increments until the remaining teeth encompass the entire proiile up to the major diameter thereof until the requisite profile or form 170 is obtained. This construction permits the rst finishing tooth 166 to take the greatest cut at the strongest part of the tooth.

The drawings and the foregoing specification constitute a description of the improved shell broach in such full, clear, concise and exact terms as to enable any person skilled in the art to practice the invention, the scope of which is indicated by the `appended claims.

What I claim yas my invention is:

1. A broach having a series of longitudinally aligned finish cutting teeth arranged in circumferentially aligned groups, the pitch between adjacent gnoups of teeth being different from the pitch adjacent thereto.

2. A broach having a series of longitudinally Ialigned iinish cutting teeth, said teeth being of less height than the height of the teeth on the workpiece, said teeth being of progressively increasing Width, corresponding edges at both sides of said teeth being circumferentially stepped so -as to cause each of said teeth to cut substantially en- Y tirely at the sides thereof, the pitch between longitudinally adjacent teeth being slightly ditte-rent from the pitch adjacent thereto.

3. A broach assembly comprising a leading section having longitudinally aligned series of progressively stepped cutting teeth, and a support portion `following said cutting teeth having a cylindlical support surface, a finishing breach shell mounted on said support surface, said shell 'i0 having longitudinally aligned series of finishing teeth arranged in circumferential groups, said finishing teeth progressively increasing in width from the front toward the rear or" the shell, the pitch between adjacent groups of teeth being different from the pitch yadjacent thereto, and means for retaining the shell on said support portion.

4. The breach assembly deined in claim 3 wherein the teeth of the iinishing shell have a double staggered pitch between adjacent groups.

5. The breach assembly defined in claim 3 wherein the teeth `ot the nishing shell have a triple staggered pitch between adjacent groups.

References Cited by the Examiner UNlTED STATES PATENTS 1,197,132 9/16 La Pronite 29-95.1 1,310,934 7/19 Suverkrop 29-95.1 X 1,806,552 5/31 Atwood 29-95.1 1,935,774 11/33 Halborg 29-95.1 1,969,977 8/34 Halborg 2995.1 2,011,630 8/35 Halborg 29-95.1 2,041,759 5/36 Halborg 29-95.1 2,060,889 11/36 Nilsson 29-95.1 2,078,632 4/37 Halborg 29-95.1 2,161,901 6/39 Praeg 29-95.l 2,330,863 10/43 Bonnafe 29-95-1 2,683,919 7/54 Psenka 29-95.1 2,898,670 8/59 Pernack 29-95.1 2,986,801 6/61 Mently 29-95.1 2,987,801 6/61 Psenk-a 29--95.1

FOREGN PATENTS 22,248 12/20 France.

414,331y 8/31.l Great Britain.

592,888 10/ 47 Great Britain.

422,705 6/47 Italy.

WILLIAM W. DYER, JR., Primary Examiner. 

1. A BROACH HAVING A SERIES OF LONGITUDINALLY ALIGNED FINISH CUTTING TEETH ARRANGED IN CIRCUMFERENTIALLY ALIGNED GROUPS, THE PITCH BETWEEN ADJACENT GROUPS OF TEETH BEING DIFFERENT FROM THE PITCH ADJACENT THERETO. 